1. Field of Invention
The present invention relates to a gas generator for a restraining device such as an airbag system in a vehicle.
2. Description of Related Art
In a pyrotechnic type gas generator using a gas generating agent, the combustion performance can be adjusted and an amount of gas generated per unit time can be changed by adjusting one or more optional factors selected among a charging amount, a shape, dimensions, composition, and a composition ratio of the gas generating agent.
For example, in order to reduce the effect for the occupant, a method is implemented by which, in an airbag deployment, a gas generation amount is adjusted to a small volume at an initial stage of combustion and to a large volume in a later stage of combustion, thereby obtaining the so-called S-shaped output curve representing pressure variations in the generated gas with time, or a method is implemented by which a gas generation rate is reduced at a later stage of combustion after the airbag has been deployed, in order to maintain the deployed state thereof.
In a gas generator 10 described in JP-A No. 2006-168670, a combustion chamber is defined outside an inner tube 16 in a housing 11, and the combustion chamber is divided into two combustion chambers (a first combustion chamber 31 and a second combustion chamber 32) by a partitioning member 26.
The combustion gas generated in the first combustion chamber 31 passes through the second combustion chamber and reaches a gas discharge port 15 formed in the circumferential wall of the housing 11.
Since communication holes 17 and 18 formed in the inner tube 16 have different opening areas, the burn-up time differs among the gas generating agents in the combustion chambers and the gas is discharged in two stages.